This is a 5-year longitudinal study of the incidence of dementia and depression in patients with idiopathic Parkinson's disease. Two hundred and fifty community residents with idiopathic Parkinson's Disease will be examined to determine the prevalence of dementia and/or depression. Phase Two will begin after the prevalence study where we will examine the remaining cohort for the incidence of dementia and depression. We will also determine the natural history of dementia and depression in idiopathic PD.